My datasource isn't updating when changing the binding list using a task

Question

I want to bind my combobox's data source using a binding list. The binding list contains a collection of Client instances. I managed this and it works well, but because reading from the database takes long I decided to use a task. And now once the binding list is updated via the task the combobox still has no values.

I wanted to use a normal thread at first, but struggled so switched to using a task(pretty much the same thing I guess thing I guess). So a solution using threads would be just as useful.

    public partial class frmJobCreation : Form
    {
        public frmJobCreation()
        {
            InitializeComponent();
        }

        BindingList<Client> clients = new BindingList<Client>();

        private void frmJobCreation_Load(object sender, EventArgs e)
        {
            cbxRtojClient.DataSource = clients;
            Task.Run(() =>
            {
                clients = new BindingList<Client>(Client.GetClients());
            });
        }
    }

Where Client.GetClients() is a static method that returns List<Client>

score 1 · Accepted Answer · edited May 23 '17 at 12:22

In the form load event you have cbxRtojClient.DataSource = clients; and then you are updating the clients object in the Task. But this is never going to update the ComboBox.

A Task in C# (wrt winforms) should ideally perform a task and return its results so that it can be updated in the UI. The UI update should ideally be done in a ContinueWith continuation task which is run in the UI context. We should always update any control in the context of the UI thread. Check this for reference.

Task.Run<BindingList<Client>>(() =>
{
    // return all the clients to 'ContinueWith' task
    return new BindingList<Client>(Client.GetClients());
})
.ContinueWith(t =>
{
    // Result is a dynamic property and holds the output of its previous Task. BindingList<Client> in this case.
    clients = t.Result;

    // Update UI
    cbxRtojClient.DataSource = clients; 
}, TaskScheduler.FromCurrentSynchronizationContext()); // ensures calling the ContinueWith task to be run in the UI thread.

To know more about Task Parallel Library (TPL) follow this.

Thank you, this worked and the link you added helped me understand why. Much appreciated. — Storm Muller, Jun 05 '16 at 12:13
Great, the combobox datasource count didn´t match with items.count , this workaround works for my problem. — elchente23, Jul 29 '20 at 06:12

My datasource isn't updating when changing the binding list using a task

1 Answers1